The present invention relates to a method of driving a plasma display panel and more particularly, to a method of driving an AC-type plasma display panel for displaying a dynamic image without intensity level disturbance and false color contours in a multi-scan driving method within a sustaining pulse period.
Recently, a plasma display panel (referred to as xe2x80x9cPDPxe2x80x9d hereinafter) has advantageous characteristics capable of being utilized as a direct-view large HDTV display apparatus having large screen size but a small thickness and a wide viewing angle compared to other flat display devices.
A PDP is classified into a two-electrode type PDP in which an address discharge and a sustain discharge are performed by two electrodes and a three-electrode type PDP in which an address discharge and a sustain discharge are performed by three electrodes.
FIG. 1 is a schematic sectional view of a discharge cell of a typical PDP and FIG. 2 is a plan view of a three-electrode type of PDP.
The discharge cell 10 of the three-electrode type PDP 1 comprises two glass plates 12 and 13 arranged to be facing each other. On the first glass plate 13 the first electrode 14 (X electrode) and the second electrode 15 (Y electrode) are formed and arranged parallel to each other. The electrodes function as sustain electrodes. The first and second electrodes 14 and 15 are covered with a dielectric layer 18. The upper surface of the dielectric layer 18 is covered with a MgO layer 21, which protects the dielectric layer 18.
On the second glass plate 12 a third electrode 16 is arranged orthogonal to the first and second electrodes 14 and 15. The third electrode functions as a data electrode. A barrier rib 17 of a lattice or stripe shape is formed between the two glass plates 12 and 13 to define a discharge cell. A phosphor material 19 is coated on the surface of the third electrode and the inner surface of the barrier rib.
As shown in FIG. 2, a PDP display device using such three-electrode type PDP comprises a plurality of X electrodes and Y electrodes arranged parallel to each other and wherein Y electrodes are driven independently by separate Y scan driving circuits 4- to 4-n coupled to a Y electrode sustain driving circuit and X electrodes are coupled in common and are driven by a common X electrode driving circuit 5.
Data electrodes 16-1 to 16-n arranged to be orthogonal to the X and Y electrodes are driven by a data driving circuit 6. Also, each of separate Y electrode scan driving circuits 4-1 to 4-n is coupled to the Y electrode sustain driving circuit 3 and generates a scan pulse and sustain pulse.
The Y electrode sustain driving circuit 3 generates a sustain discharge pulse and the generated sustain discharging pulse is applied to the Y electrodes 15-1 to 15-n via the separate Y scan driving circuits 4-1 to 4-n.
The common X electrode driving circuit 5 generates a sustaining pulse which is applied to the X electrodes.
The driving circuits 3, 5 and 6 are controlled by a control circuit (not shown) which is in turn controlled sequentially by a synchronization signal and then a display data signal. In FIG. 2, numeral 1 denotes a PDP and numeral 10 denotes a cell constructing the PDP 1.
There have been proposed several driving methods for a multi-gradation display of such plasma display device. As an example, U.S. Pat. No. 5,541,618 (assigned to Fujitsu Limited.) discloses a driving method in which a frame displaying a single picture is divided into a plurality of subfields and each of the subfields is separated in an addressing period and a sustain period and in each of the subfields, after addressing, a sustaining operation is carried out to all display electrodes at the same time.
FIG. 3 shows a frame structure illustrating a conventional driving method. When scan lines are 480, a frame of a single picture is divided into eight subfields, and a time taken to perform an addressing operation within a frame of a single picture is approximately 11 to 12 microseconds.
Substantially, since a display time (sustaining time) when a viewer can view an image is approximately 5 to 6 microseconds, a display period (sustaining period) that contributes to the brightness of an image is only approximately 30%, resulting in a deterioration of picture brightness. In this case, increasing a frequency of sustain pulse in order to compensate for such deterioration of image brightness can be considered, however, it also causes an increase of the power consumption and a deterioration of driving reliability.
The present applicant has suggested a new driving method capable of solving such problems encountered by the conventional driving method (see PCT/KR98/00204 filed in the name of the present applicant). According to a basic feature of the above-suggested driving method, a frame is divided into a plurality of subfields, and display lines corresponding to the total number of the divided subfields are selected. Then, scan pulses corresponding to the total number of the divided subfields are applied sequentially within a single sustain pulse applied to Y scan sustain electrodes and thereby cells of selected display lines to be displayed are designated. Thereafter, the designated cells of selected display lines are displayed by the following sustain pulse.
Next, after one sustain pulse period, display lines which are downwardly or upwardly shifted from the above selected display lines by one line are selected. Then, scan pulses corresponding to the total number of the divided subfields are applied sequentially within a single sustain pulse applied to Y scan sustain electrodes and thereby cells of selected display lines to be displayed are designated. Thereafter, the designated cells of selected display lines are displayed by following sustain pulse. Continuously, by repeating the display of the subfields for the display lines by shifting one line as a unit one sustain pulse period until each of the subfields for all display lines are completely displayed, the display for a frame is completed.
In this manner, a feature of the above driving method enables scanning of other display lines simultaneously by sustaining them. In order to realize it most suitably, the number of sustain pulses for one frame should be set to be equal to that of the display lines. Also, when selecting display lines, positioning of selected display lines should be determined by considering the number of sustain pulses for each of the subfields.
Now, a feature of the above driving method will be described in detail with reference to FIGS. 4 and 5. For convenience of the description, it assumed that a single frame is divided into three subfields (SF1, SF2, and SF3) and display lines are 7 lines (D1 to D7). Accordingly, it is possible to establish sustain periods in subfields SF1, SF2, and SF3 to 1, 2 and 4, respectively.
Also, regarding the position of the display line selected firstly, it is possible to select the display lines D1, D3 and D7 in consideration of the sustain periods set for the subfields SF1, SF2 and SF3. In FIG. 4, S1 to S7 represent sustain periods.
As shown in FIG. 4, firstly, display lines D1, D3 and D7 are selected, and then the display of the subfields SF1, SF2 and SF3 for display lines D1, D3 and D7 are executed respectively. Next, selecting display lines D2, D4 and D1, which are allocated downwardly by one display line from the above selected display lines D1, D3 and D7, and then the display of the subfields SF1, SF2 and SF3 for display lines D2, D4 and D1 are executed respectively. Next, selecting display lines D3, D5 and D2, which are allocated downwardly by one display line from the above selected display lines D2, D4 and D1, and then the display of the subfields SF1, SF2 and SF3 for display lines D3, D5 and D2 are executed respectively. Next, selecting display lines D4, D6 and D3, which are allocated downwardly by one display line from the above selected display lines D3, D5 and D2, and then the display of the subfields SF1, SF2 and SF3 for display lines D4, D6 and D3 are executed respectively. Next, selecting display lines D5, D7 and D4, which are allocated downwardly by one display line from the above selected display lines D4, D6 and D3, and then the display of the subfields SF1, SF2 and SF3 for display lines D5, D7 and D4 are executed respectively. Next, selecting display lines D6, D1 and D5, which are allocated downwardly by one display line from the above selected display lines D5, D7 and D4, and then the display of the subfields SF1, SF2 and SF3 for display lines D6, D1 and D5 are executed respectively. Finally, selecting display lines D7, D2 and D6, which are allocated downwardly by one display line from the above selected display lines D6, D1 and D5, and then the display of the subfields SF1, SF2 and SF3 for display lines D7, D2 and D6 are executed respectively.
At this time, the display of a previous frame for each of the display lines is completed together with selecting display lines for displaying the next frame, and then the display of the subfields of the next frame for display lines are executed. Thereby, the display of the subfields of the next frame and the display of the subfields of the previous frame are overlapped at the same time. In FIG. 4, when display lines D2, D4, D5 and D6 display subfields SF2, SF3, SF3 and SF3 of the previous frame, respectively, other display lines D1, D3 and D7 display subfields SF1, SF2 and SF3 of the next frame, respectively.
FIG. 5 is a pulse waveform diagram applied to each electrode in order to display the frame as shown in FIG. 4, and illustrates a driving in accordance with a select erase scheme.
First, display lines D1, D3 and D7 whose number is identical to that of the divided subfields are selected, and then the display of the subfields SF1, SF2 and SF3 for the selected display lines D1, D3 and D7 are executed respectively. In other words, by applying a negative write pulse to Y electrodes (Y1, Y2 and Y3) constituting the selected display lines D1, D3 and D7 and applying a positive pulse to common X electrodes, a write discharge for all cells of the selected display lines D1, D3 and D7 is performed.
Thereafter, within one sustain period, scan pulses generated from Y scan-driving circuit are sequentially applied to the selected Y electrodes (Y1, Y2 and Y3). At the same time, data pulses generated from the data driving circuit in accordance with input image data to be displayed are applied to the data electrodes.
If explaining the above state using a discharging principle, as a result of the above write discharge, (+) wall charge is accumulated on a dielectric layer covering Y electrodes and (xe2x88x92) wall charge is accumulated on a dielectric layer covering common X electrodes. Then, if applying a scan pulse and data pulse thereto, the accumulated wall charge is erased. Accordingly, the wall charge on the display lines applied data pulse is erased. Thus, even though a sustain pulse is applied to the common X electrodes and Y electrodes, sustain discharge between the common X electrodes and Y electrodes is not performed. However, since the wall charge is accumulated on the display line to which no data pulse is applied, sustain discharge is performed.
Next, in the next sustain period, the negative write pulses and the positive pulse are applied to the Y electrodes (Y2, Y4, and Y1) and the common X electrode of display lines D2, D4 and D1 respectively, which is allocated downwardly by one display line from the above selected display lines D1, D3 and D7. Then, scan pulses generated from the Y scan-driving circuit are sequentially applied to the selected Y electrodes (Y2, Y4 and Y1). At the same time, data pulses generated from the data driving circuit in accordance with the input image data to be displayed are applied to the data electrodes. At this time, by applying the write pulses to the Y electrodes (Y2, Y4 and Y1) of the display lines (D1, D3 and D7) which are selected in the next sustain pulse period, the display of the selected display line (D1) in the previous sustain pulse period is finished. As a result, the display of a subfield (SF1) for the selected display line (D1) in the previous sustain pulse period is completed. In this way, setting of each of the subfields to each of the selected display lines is determined in advance in accordance with the position of the display lines selected firstly.
Continuously, by repeating the display of the subfields for the selected display lines by shifting one line as an unit of one sustain pulse period until each of the subfields for all display lines is completely displayed, the display for a frame is completed. Finally, the display lines, which have completed all subfields of one frame, will end their sustain discharges by applying a write pulse to display subfields of the next frame.
Accordingly, since within the period of one frame, it can perform simultaneously addressing (scan) of another display line during sustain period of one display line, such driving method can perform display with high efficiency.
As shown in FIGS. 4 and 5, however, such driving method has a problem that during at least a predetermined time, continuous two frames are displayed simultaneously. That is, as shown in FIG. 5, before finishing completely an image display of the first frame F1, an image display of the second frame F3 is performed.
As a result, a mixing display period FH is produced, resulting in an incorrect image display of one frame. Also, there may be caused a problem of image distortion that when displaying a dynamic image, images in two frames are viewed as overlapped to a viewer.
In addition, a general driving method is limited to a fixed sequence in which a sequence of driving each of subfields and the number of subfields is predetermined, and these sequences become identical along the time axis. Accordingly, there is frequently caused a repeated occurrence of a specific gray level when displaying a dynamic image. If such occurrence arises in an area in which a bit carrier exists, a low frequency component is generated in the form of a partial flicker, resulting in a deterioration of image quality.
Now, the driving method will be described in more detail with reference to FIG. 6.
First, it is assumed that one frame is divided into eight subfields SF1, SF2 . . . SF8 and sustain pulses are set as 1, 2, 4, 8, 16, 32, 64 and 128, respectively and that thereafter, by combining suitably these subfields, gray level of 28=256 are displayed.
The 63rd gray level lights-on all the subfields SF1 through SF6 and the 64th gray level lights-on only subfield SF7. As shown in FIG. 6, when light on occurs repeatedly at the 63rd gray level and the 64th gray level for every frame, the human eyes view the 127th gray level and the 0 gray level as light on repeatedly every frame. Thus, there occurs the problem that a low frequency component is formed for two adjacent frames and thusly a flicker is generated.
Furthermore, if scrolling a display of gray level in the inclined direction of brightness when displaying a dynamic image, a bright line and a dark line occur in a specific gray level and thusly the dynamic image is displayed as a false contour
Accordingly, an object of the present invention is to provide a driving method capable of preventing images in two frames from being viewed overlapping to a viewer when displaying a dynamic image by clarifying a boundary between adjacent frames in a multi-scan driving method within a sustaining pulse period.
Another object of the present invention is to provide a driving method capable of reducing an occurrence of a flicker and a false contour in a multi-scan driving method.
According to the present invention, there is provided a method of displaying a halftone image on a PDP display unit by using a frame division technique that divides each frame of halftone image into subfields with each having specific sustain pulses to provide a specific intensity level, comprising:
selecting display lines whose number is identical to the total number of said divided subfields, the position of said selected display lines being determined based on the number of sustain pulses set previously to said each subfields, addressing for designating pixels of selected display lines to be displayed and displaying each subfield allocated for the said selected display lines;
shifting by a predetermined number of display lines from said selected display lines as a sustain pulse period unit, selecting display lines, addressing for designating pixels of selected display lines to be displayed and displaying each subfield allocated for the said selected display lines; and
repeating said shifting, said selecting, said addressing and said displaying steps until each of the subfields is completely displayed with regard to all display lines;
wherein display lines for all subfields of one frame have been completely displayed within an idle period, during which a subfield of the following frame is not displayed.
Moreover, the method is characterized in that said idle period is started by applying an erase pulse to the display lines where the display for all subfields has been already completed.
Also, the method is characterized in that the positions of the display lines which are firstly selected to display subfields of the following frame after completely displaying a previous frame are determined different from those of display lines which are firstly selected to display subfields of the previous frame.